Received 02/26/2020 Review began 03/02/2020 Review ended 03/19/2020 Published 04/10/2020

© Copyright 2020Wardhan et al. This is an openaccess article distributed under theterms of the Creative CommonsAttribution License CC-BY 4.0., whichpermits unrestricted use, distribution,and reproduction in any medium,provided the original author andsource are credited.

The Challenges of Ultrasound-guidedThoracic Paravertebral Blocks in RibFracture PatientsRicha Wardhan , Sowmya Kantamneni

1. Anesthesiology, University of Florida, Gainesville, USA 2. Anesthesiology, Veterans Affairs PugetSound Health Care System, University of Washington, Seattle, USA

Corresponding author: Richa Wardhan, richawardhan@gmail.com

AbstractThoracic paravertebral blocks (TPVBs) provide an effective pain relief modality in conditionswhere thoracic epidurals are contraindicated. Historically, TPVBs were placed relying solely onthe landmark-based technique, but the availability of ultrasound imaging makes it a valuableand practical tool during the placement of these blocks. TPVBs also provide numerousadvantages over thoracic epidurals, namely, minimal hypotension, absence of urinaryretention, lack of motor weakness, and remote risk of an epidural hematoma. Utilization ofboth landmark-based and ultrasound-guided techniques may increase the successful placementof a TPVB. This article reviews relevant sonoanatomy as it pertains to TPVBs. However, certainpatient-related issues, including pneumothoraces, surgical emphysema, body habitus, andtransverse process fractures, all may make imaging with ultrasound challenging. The changesnoted on ultrasound imaging as a result of these issues will be further described in this review.

Categories: Anesthesiology, TraumaKeywords: ultrasound, rib fractures, nerve block, thoracic paraverterbral block, chest trauma

Introduction And BackgroundThoracic paravertebral block (TPVB) is an effective technique for pain management in patientswith rib fractures. Even though thoracic epidurals are considered the gold standard for thispatient population, the use of low-molecular-weight heparin (LMWH), spine, and other bonyfractures preclude the utilization of thoracic epidurals in this group of trauma patients [1].TPVBs have an important role to play when epidurals are not a good fit.

TPVBs can be placed by landmark-based techniques or with the help of ultrasound(US). Available literature suggests that TPVBs may be performed with a high probability ofsuccess using US guidance as an adjunct to traditional techniques [2]. However, there is apaucity of data on the use of real-time US guidance for the TPVBs. In fact, due to a lack ofstudies, Abrahams et al. gave a grade B level of evidence recommendation for the use of US toplace paravertebral blocks based on two small case series. They further stated that there wasinsufficient evidence to show that US guidance improved block success rates or reduced the riskof complications compared with traditional techniques for performing single-shot orcontinuous paravertebral blocks [2].

ReviewWhile US guidance is ideal in the rib fracture patient population to avoid TPVB-associatedcomplications, such as pneumothorax/hemothorax, US-guided TPVBs have their own

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Open Access ReviewArticle DOI: 10.7759/cureus.7626

How to cite this articleWardhan R, Kantamneni S (April 10, 2020) The Challenges of Ultrasound-guided Thoracic ParavertebralBlocks in Rib Fracture Patients . Cureus 12(4): e7626. DOI 10.7759/cureus.7626

challenges in this subgroup. Factors that compromise successful placement of US TPVBsinclude pneumothorax, surgical emphysema from subcutaneous air, morbid obesity, technicalissues like an ultrasound device with low resolution, blood or fracture in the intercostal space,and morbidly obese patients [3].

To better comprehend these issues, it is important to understand the sonoanatomy of thethoracic paravertebral space (TPVS) and the technical aspect of placing US-guided TPVBsdemonstrated herein on healthy volunteers.

US-guided TPVBs can be performed using two approaches: 1) a parasagittal approach and 2) anintercostal approach.

For the parasagittal approach, a low, curved low-frequency (in obese patients) or a high-frequency linear array ultrasound probe is placed longitudinally, such that the long axis of theprobe is parallel to the midline (Figure 1). The position can be sitting or lateral decubitus(Figure 2). The probe is used to scan starting from the midline, identifying the spinousprocesses and then the lamina, followed by the transverse processes. The pleura appears as anechogenic, shimmering structure in between the transverse processes (Figure 3). The midpointof the transducer is then aligned midway between the two adjacent transverse processes. Localanesthesia is infiltrated at the superior edge of the probe. Using an in-plane approach, an 18-gTuohy needle is inserted and advanced between the costotransverse ligament and thepleura (Figure 2). Five mL of ropivacaine 0.5% can be then injected after careful aspiration, anda multi-holed epidural catheter threaded 4 - 5 cm into the space.

FIGURE 1: Scanning technique to obtain theparasagittal/longitudinal view on a healthy volunteera, b) The probe is positioned in the midline longitudinal plane showing spinous processes (SP); c,d) The probe is positioned in the paramedian longitudinal plane depicting the lamina (white arrow);e, f) Moving the probe further lateral shows the transverse processes (TP), pleura (P), andparavertebral space (white arrows)

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FIGURE 2: Parasagittal needle approach depicted on a healthyvolunteerParavertebral blocks showing the orientation of a low-frequency probe in the longitudinal plane withthe needle approaching cephalad to the probe

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FIGURE 3: Ultrasound view of paravertebral space (red arrow)in the parasagittal view showing two transverse processes(TP) and pleura (P) in a healthy volunteer.

For the intercostal approach, we follow the technique described by Shibata et al. [4]. Theposition can be either sitting or lateral decubitus. A high-frequency linear array probe orcurvilinear low-frequency probe (depending upon the body habitus) is placed on the rib at theselected level. The medial edge of the probe is kept close to the spinous process in order to viewthe transverse process (Figure 4). In this position, the horizontal view of the rib is visualized asa hyperechoic line. The probe is then moved caudally into the intercostal space betweenadjacent ribs. In this acoustic window, the inferior part of the transverse process can bevisualized as a hyperechoic convex line. The apex of the TPVS is visualized as a wedge-shapedhypoechoic space. The TPVS lies enclosed by the hyperechoic line of the pleura below and theinternal intercostal membrane above. The apex of TPVS is laterally continuous with theintercostal space (Figure 5). An 18-gauge Tuohy needle is inserted in a lateral-to-medialdirection using an in-plane approach and advanced until the needle tip penetrates through theinternal intercostal membrane. After a negative aspiration test for blood, 5 mL of localanesthetic is injected into the TPVS slowly and a multihued epidural catheter is threaded 4 - 5cm in the space. The pleura is seen being pushed ventrally during a local anesthetic injection[4].

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FIGURE 4: Intercostal placement of the ultrasound for aparavertebral block with the needle approaching lateral tomedial shown here on healthy volunteer

FIGURE 5: Ultrasound view of the paravertebral space (redarrow) in the intercostal view showing the transverse process(TP) and pleura (P)Spinous process (SP) and lamina (white arrow) are also seen in this view obtained from a healthyvolunteer.

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Pneumothorax (PNX)The presence of PNXs in patients with rib fractures is a common occurrence. Ultrasoundimaging has been utilized by emergency medicine and critical care physicians to detect PNX formore than two decades now. An ultrasound allows the detection of small amounts of loculatedpleural fluid in amounts as small as 20 mL, which cannot be identified by x-rays, as it is onlycapable of detecting volumes above 50 mL [5]. The knowledge of an ultrasound-guided lungexamination is also helpful for a regional anesthesiologist to identify an occult PNX as thiscould affect the placement of ultrasound-guided paravertebral blocks.

The presence of PNX is determined on the basis of accepted sonographic criteria [6]:

1. Disappearance of lung sliding (Figure 6)

2. Identification of the lung point (Figure 6)

FIGURE 6: Ultrasound of the third intercostal space along theanterior axillary lineThe lung point (ultrasound of the 3rd intercostal space along the anterior axillary line).

A) Expiration. Absence of lung sliding, plus A-lines; B) M-mode shows the sudden (arrow)inspiratory appearance of the lung point.

Permission to use this figure obtained by Lichtenstein et al. [7]

The visualization of lung sliding on the anteroinferior chest wall in the supine patient has a

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100% negative predictive value in the diagnosis of PNX [6]. Lung sliding refers to theshimmering appearance of the pleura caused by rubbing of the parietal and visceral pleura oneach other on the ultrasound image. When air separates the two pleural layers, the movementdisappears and cannot be detected, and the parietal pleura is still visualized but does not move[8]. The presence or absence of the dynamic pleural lung sliding, captured on a single staticimage, can be further verified using a power color Doppler. The absence of a power colorDoppler signal (coined the “power slide”) at the thoraco-pleural interface may serve as acriterion in the identification of a PNX [9].

Horizontal, regularly spaced, hyperechogenic lines representing reverberations of the pleuralline are called ultrasound A-lines; narrow-based comet-tail artifacts arising from the pleuralline and spreading up to the edge of the screen are ultrasound B-lines. Absent lung sliding, plusexclusive A-lines, are suggestive of pneumothorax.

An absent sliding sign does not always signify that a PNX is present. In critically ill patients, itmay just represent the presence of atelectasis. Knowledge of identifying B-lines, also calledcomet tail artifacts, can be very helpful in such situations. B-lines arise from the pleural lineand spread vertically like echogenic rays. They reach the lower edge of the screen withoutwaning and move with the respiratory movements [8]. It may indicate other lung pathology(such as thickened interlobular septa in the interstitial syndromes, like pulmonary edema andlung contusions), but visualization of B-lines rule out PNX with a true negative rate of 100% [8,10].

The absence of both lung sliding and B-lines in the anteroinferior chest area suggestspneumothorax. Moving the ultrasound to the inferolateral chest wall looking for the “lungpoint” (which is a point where lung sliding or B-lines are visualized again) confirms thediagnosis of PNX [6].

It is important for the operator performing the ultrasound-guided paravertebral block torecognize a PNX using the criteria above. The presence of lung sliding helps the operator todetermine the exact location of the paravertebral space which lies superior to the pleura (extra-pleural) on the ultrasound image. However, the absence of a sliding sign can lead to confusionin identifying the pleura accurately, thus making it difficult to identify the paravertebral space.In this situation, depending upon the amount of air, the probe can then be moved to explore anintertransverse process window cephalad or caudad to place the block where pleura seems moreidentifiable.

Surgical emphysemaPatients with rib fractures and accompanying PNX often present with surgical emphysema. Thepresence of surgical emphysema presents unique challenges when performing an ultrasound-guided paravertebral block. First, surgical emphysema interferes with the ultrasoundinterpretation of a pneumothorax. Second, strong reflections or echoes show on the ultrasoundimage as white and weaker reflections as gray. A soft tissue air boundary reflects 99% of thebeam, thus none is available to reflect back to the probe [11].

All the above factors degrade the ultrasound image, leading to poor visualization of targetedarea and inability or difficulty in performing an ultrasound-guided procedure. Saranteas et al.presented two case reports where the presence of subcutaneous air and surgical emphysemaresulted in difficulty in the visualization of the structures below [12]. In the medical literature,authors have reported difficulty in obtaining central line access due to the presence of air in thetissues [13].

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Unfortunately, there is not much that can be done if the air obscures the image, other thanscanning cephalad to caudad to identify areas where the visualization is better. The operatorcan then utilize these specific windows to image the space. Alternately, using a landmarkapproach to place the block may be the only option.

ObesityObesity is a major medical problem and presents unique challenges for a proceduralist. Whiletechnology has come a long way over the past years with the development of new machines,many shortcomings still exist.

Ultrasound is an important imaging modality that is limited by user experience and skill, aswell as patient body habitus and comorbidity. A higher frequency allows for better resolutionwhile sacrificing penetration. This poses a challenge for the physician using ultrasound toperform a nerve block on an obese patient. To clearly visualize structures deeper to the extrasubcutaneous adipose tissue, lower frequencies need to be used which results in poorresolution and, therefore, poor quality of the images. The problem here is evident - poor imagequality leads to more difficult regional blocks, which ultimately leads to higher failure rates andincreased complications. This problem is amplified in trauma patients where (due to the injurysuffered by the patient) the anatomy is altered, leading to even more confusion by thepractitioner on what the image is showing.

Obesity increases the acoustic path length, requiring a greater depth of penetration to view atarget. Obesity may also have an indirect effect on the underlying muscle thickness and tone[14].

Imaging is degraded in obese individuals due to the following phenomena:

1) Sound attenuation: The ultrasound beam is weakened as it travels through the adiposetissue. The higher the frequency of the probe, the more attenuation is seen [15].

2) Phase aberration of the sound field reduces the quality of the ultrasound because of theuneven speed of sound in the irregular layers of adipose [16].

The following tips provide a better resolution while using ultrasound [17]:

1) Using a low-frequency transducer counteracts sound attenuation,

2) Compressing the tissues with the transducer brings the target in better focus,

3) Using a large beamwidth of the ultrasound signal,

4) Utilizing advanced technology, like tissue harmonic imaging, aiding in better tissuepenetration [18].

Transverse process fractures (TVPFX)Thoracolumbar spine TVPFXs are markers of major torso trauma and indicate a high-energymechanism. They may have pulmonary or gastrointestinal dysfunction related to their injuries[19].

Even though they are considered not as painful as rib fractures, they can still cause significantpain requiring careful pain management. TVPFXs can disturb the integrity of the paravertebral

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space. A TVPFX appears as a gap in the cortex of the rib and may be associated with a localizedhematoma, effusion, or soft tissue swelling. Ultrasonography can visualize the costal cartilage,as well as the osseous part of the rib [20].

A paravertebral block (PVB) at the spinous level of a fractured transverse process can beunreliable and difficult due to the presence of bony fragments and/or hematoma. However, inour experience, these patients benefit tremendously from the nerve blocks, even if a successfulPVB is not achieved. This may be due to the spread of local anesthetic directly at the site oftrauma.

Whenever feasible, continuous paravertebral catheters should be placed instead of a singleinjection since the pain from rib fractures affects the patient acutely for several days. Patientsaged 65 years or older with two or more rib fractures, those with preexisting pulmonarydisease, and patients with evidence of an increased effort of breathing/splinting are goodcandidates for paravertebral catheters [21]. Multimodal pain management, including non-steroidal anti-inflammatory drugs (NSAIDs), acetaminophen, and short-acting opioids, shouldbe strongly considered.

ConclusionsIn conclusion, US-guided TPVB is a useful and safe technique of providing adequate pain reliefin rib fracture patients. These patients have significant pain management needs and require aspecialized effort in mobilization, reasonably extending their hospital stay. Since there is a lackof considerable data for ultrasound-guided paravertebral techniques, no studies or reviewarticles have elaborated on the use of ultrasound-guided paravertebral block in rib fracturepatients. We hope that this article is able to shed more light on this matter and enable readersto make an educated decision when faced with these challenges.

Additional InformationDisclosuresConflicts of interest: In compliance with the ICMJE uniform disclosure form, all authorsdeclare the following: Payment/services info: All authors have declared that no financialsupport was received from any organization for the submitted work. Financial relationships:All authors have declared that they have no financial relationships at present or within theprevious three years with any organizations that might have an interest in the submitted work.Other relationships: All authors have declared that there are no other relationships oractivities that could appear to have influenced the submitted work.

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